Revenge is a dish best eaten cold.

The earliest located appearance is in an 1841 French novel by Eugène Sue, where a character remarks that revenge is best eaten cold and explicitly frames it as a common, already-existing saying rather than a personal invention. The expression then appears in English in the 1840s via reviews, fiction, and translations, and later gets attached to various famous figures and even labeled as a Roman proverb, but those attributions arise after the phrase was already in circulation.

The proverb suggests that retaliation is more effective when delayed until emotions cool and circumstances can be chosen strategically, rather than pursued immediately in anger.

Et puis la vengeance se mange très-bien froide, comme on dit vulgairement . . .

Revenge is a dish best eaten cold

Revenge is a dish best served cold

Vengeance is best eaten cold

Vengeance should be eaten cold